Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$40.50	10.837%	$44.889	$44.89	$44.90	$44.90
Purchase #2	$188.87	7.437%	$202.9163	$202.92	$202.90	$202.90
Purchase #3	$36.88	8.233%	$39.9163	$39.92	$39.90	$39.90
Purchase #4	$244.89	5.680%	$258.7998	$258.80	$258.80	$258.80
Purchase #5	$145.72	13.815%	$165.8512	$165.85	$165.85	$165.90
Purchase #6	$222.40	10.858%	$246.5482	$246.55	$246.55	$246.50
Purchase #7	$164.25	12.715%	$185.1344	$185.13	$185.15	$185.10
7 purchase totals =	$1,043.51		$1,144.0552	$1,144.06	$1,144.05	$1,144.00